[crac] RFR: Resize ForkJoinPool and some concurrent data structures

[Radim Vansa]

Some parts of JDK expect that #cpus is constant; update those places after restore.

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Commit messages:
 - Allow changes to NCPU
 - Resize ForkJoinPools when number of CPUs changes

Changes: https://git.openjdk.org/crac/pull/54/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=54&range=00
  Stats: 322 lines in 7 files changed: 292 ins; 17 del; 13 mod
  Patch: https://git.openjdk.org/crac/pull/54.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/54/head:pull/54

PR: https://git.openjdk.org/crac/pull/54